The present invention relates to marine vessels, particularly to sailing vessels, and also relates to hull assemblies and structures for sailing vessels.
There are two distinctly different ways that a moving vessel is supported by the water. When a vessel is moving slowly, the forces that are caused by moving water bending around the vessel, are small, and the hulls are supported by buoyant forces.
The hulls which present the least drag for a given weight, when moving slowly are smoothly rounded on both ends. Such hulls are called displacement hulls. When displacement hulls move at significant speed, their rounded ends behave like inverted airplane wings. That is, water flowing around the curved ends of the hull creates a partial vacuum. This vacuum pulls the rounded stern deeper into the water, making the water curve further, thereby increasing drag.
As a result of this phenomenon, displacement hulls exhibit a maximum hull speed. For practical purposes this maximum hull speed is equal to 1.4 times the square root of the hull's length. In lieu of this principle of mechanics, longer and narrower displacement hulls will generally experience less drag and a faster maximum speed.
Hulls which have a relatively large substantially flat surface that is almost parallel to the surface of the water, and are also squared at the aft edge, are called planing hulls. Planing hulls will exhibit far greater drag at very low speeds; however, at higher speeds they do not experience a very significant increase in drag. Indeed, they plane over the surface of the water and will go as fast as their motive force propels them. The practical upper speed limit for planing hulls is reached when waves cause the vessel to jump out of the water, far enough that the vessel fails to come down safely.
A practical sailboat hull must move efficiently in situations wherein the wind only provides enough motive force for low speed displacement motion. For this reason, the vast majority of sailboat hulls are purely displacement designs. There are few practical single hull boats that can plane in a very strong wind, and, there are no known planing multihulled sailboats.
Heretofore displacement boats have been provided with multiple, spaced-apart hulls or pontoons. The common catamaran and the trimaran are typical examples of this approach. Various proposals have been advanced to employ tetrahedral space frames in the construction of multihulled sailboats. These tetrahedral space frames include three elongated spars and an elongated mast extending outwardly from a central juncture. The mast extends upwardly from the central juncture, whereas the spars project outwardly and downwardly from the juncture. Additional bracing elements interconnect the ends of the spars and mast remote from the juncture. These additional bracing elements extend generally along the edges of the tetrahedron. These bracing elements cooperate with the mast spars and other elements to provide a rigid space frame. Pontoons are attached to the spar ends at the lowermost vertices of the tetrahedron.
Tetrahedral space frame structures of this general nature are disclosed, for example, in U.S. Pat. Nos. 3,831,539; 3,991,694; 4,333,412; 4,316,424; and 4,524,709. Because the tetrahedral spaceframe is supported at widely spaced points on the water surface, it has very good stability in the rough seas, and extraordinary resistance to heeling moments. The basic nature of the tetrahedral space frame provides far superior strength for a given weight. Therefore it can be bigger and can carry more sail at a given weight in a given wind, than conventional designs.
While several embodiments of tetrahedral spaceframe boats promise to find extensive utilization; there are disadvantages that are inherent in their basic geometry. The pontoons or hulls must be short, relative to the vessel's over all length, unless further structural elements are added. The addition of these elements add to the weight cost and complexity of the vessel. Also, the spars and mast cause significant wind drag.